1. Field of the Invention
The present invention relates to a flame-retardant copolyester polymer dyeable with a cationic dye, a method of producing the same, and a copolyester fiber using the same. The copolyester polymer includes terephthalic acid (hereinafter, referred to as “TPA”) as a raw material, and thus, it has excellent dyeability due to the cationic dye under atmospheric pressure while assuring excellent intrinsic physical properties of poly(ethylene terephthalate) (hereinafter, referred to as “PET”), has an increase of pack pressure, considered as a cause of reduction in spinnability during a spinning process, that is similar to that of conventional polyester, and has excellent flame retardancy.
More particularly, the present invention pertains to a method of producing a copolyester, which is capable of being dyed using a cationic dye under atmospheric pressure, assures a slow increasing speed of pack pressure because contents of foreign materials, such as unreacted materials, increasing the pack pressure in a polymer, are very low, resulting in excellent processability, and has a limited oxygen index (hereinafter, referred to as “LOI”) of 26 or more as a standard of flame retardancy in the course of producing a fiber. Additionally, unlike conventional PET, the polymer of the present invention can be dyed by cationic dye, can have vivid colors, and can assure a two tone effect after the dyeing when it is used in conjunction with a typical flame-retardant copolyester fiber, and thus, the polymer of the present invention having excellent flame retardancy and dyeability can be used in various applications.
2. Description of the Prior Art
A PET fiber is a polymer material, which has excellent mechanical properties and resistances to chemicals and environments, thereby being usually applied to fibers for clothes, industrial fibers, and films. However, even though it has some advantages, in the case of employing it as the fibers for clothes, since it has no functional groups affecting the dyeing, it can be dyed using only a disperse dye at high temperature and pressure. Accordingly, many studies have been conducted to improve dyeability by copolymerization using ionic materials.
Additionally, since the PET fiber having the LOI of 20-22 combusts in atmospheric air, it is problematic in terms of stability. With respect to this, studies have been conducted to improve flame retardancy according to a growing demand for flame retardancy in advanced countries, such as Europe and America.
The above studies are as follows.
1. The Improvement in the Dyeability by Copolymerization Using the Ionic Materials
WO 99/09238 discloses a method of producing a copolyester dyeable by a cationic dye, in which an ester-forming sulfonate compound is copolymerized in a copolymerizing ratio of 0.5-5 mol %, and which adopts a DMT process. However, the DMT process is disadvantageous in terms of productivity and production costs in comparison with a TPA process, and in practice, when it is applied to TPA polymerization devices usually used in most polyester enterprises, spinning efficiency is reduced because of the large amount of unreacted materials.
2. The Improvement in the Flame Retardancy
A method of giving the flame retardancy to a polyester fiber is classified into a first method, in which a surface of a fiber is treated with a flame retardant, a second method, in which a flame retardant material is used during a spinning process, and a third method, in which copolymerization is conducted with the use of a flame retardant material. The first method has a disadvantage of poor durability even though it is advantageous in terms of production costs. The second method includes a blend-spinning method employing a flame retardant material (flame retardant) and another blend-spinning method employing a flame-retardant master batch, which contains an excess amount of flame retardant, but the former is problematic in that spinnability and physical properties of a grey yarn are reduced, and the latter has disadvantages in that it is difficult to produce the flame-retardant master batch so that it has desired physical properties, such as viscosity and color. The third method relates to the production of flame-retardant polyester through copolymerization, and has advantages in that flame-retardant polyester has desired durability and the third method is similar to a typical method of producing polyester. A halogen-based flame retardant (mostly consisting of bromine(Br)-based flame retardant) and a phosphorus(P)-based flame retardant are usually used in the course of producing flame-retardant polyester.
Use of the bromine-based flame retardant is disclosed in Japanese Pat. Laid-Open Publication Nos. Sho.62-6912, Sho.53-46398, and Sho.51-28894, in which, since bromine-based compounds are easily decomposed by heat at high temperatures, a great amount of flame retardant must be used to obtain desired flame retardancy, and thus, the above patents are problematic in that colors of polymers deteriorate, resistance to light is reduced, and toxic gases are generated during combustion.
Furthermore, use of the phosphorus-based flame retardant is disclosed in U.S. Pat. Nos. 3,941,752, 5,399,428, and 5,180,793, and Japanese Pat. Laid-Open Publication No. Sho.50-56488, in which, in the case of the reactive flame retardant, since a phosphorus atom having a flame-retardant function is bonded to a main chain of a polymer, physical properties are reduced due to hydrolysis in the course of post-processing a polyester fiber, particularly dyeing it. Additionally, Japanese Pat. Laid-Open Publication No. Sho.52-47891 discloses the production of flame-retardant polyester, in which a phosphorus-based flame retardant is used in a predetermined stage of an ester interchange reaction and a polycondensation reaction. However, in the case of employing dimethyl terephthalate (hereinafter, referred to as “DMT”) as a raw material, there are some problems that production costs are high in comparison with that of a terephthalic acid (hereinafter, referred to as “TPA”) process and a polymer produced through this Japanese patent is degraded by UV.
As described above, conventionally, studies have been conducted to improve the dyeability and to provide flame retardancy by copolymerization of the ionic materials. Recently, there is a growing need to add flame retardancy to intrinsic physical properties according to a growing demand for bedclothes, interior fiber products, and clothes having flame retardancy in advanced countries.
A method of physically blending a flame-retardant polyester polymer and a polyester polymer dyeable with a cationic dye during a spinning process may be suggested to produce a flame-retardant fiber dyeable with a cationic dye, to be provided by the present invention. However, this method is problematic in that since a copolyester fiber produced according to the method includes two polymers simply blended with each other, a content of phosphorus, acting as the flame retardant, is reduced, and thus, the desired flame retardancy is not assured, and that since a content of the ionic materials, which provide dyeability by the cationic dye, is reduced, the dyeability by the cationic dye is reduced due to a reduction in spaces to be dyed by the cationic dye. Additionally, it is difficult to precisely regulate contents of the flame retardant and ionic materials, and to uniformly disperse them, resulting in nonuniform physical properties of a grey yarn.